Necroptosis induced by MLKL overexpression in liver triggers cellular senescence and leads to chronic inflammation and fibrosis.

Abstract

Cellular senescence and necroptosis are two cell fates, which trigger an inflammatory response and increase with age, that have been proposed to play a role in inflammaging. In this study, we performed the first study to directly test the possible interaction between necroptosis and cellular senescence. Using a novel Mlkl-KI mouse model, we were able to specifically induce (~ 4-fold) the overexpression of MLKL, the necroptotic executioner, in hepatocytes (hMlkl-KI mice). The overexpression of MLKL led to increased necroptosis and cell damage/death in liver, as shown by increased levels of MLKL-oligomers, TUNEL staining, and Ki-67 staining in the livers, as well as increased ALT activity and HMGB1 levels in the plasma. The increase in necroptosis was paralleled by an increase in cellular senescence. We observed increased levels of p16and p21as well as SASP-factors. As expected, inflammation, as measured by the levels of proinflammatory factors and mononuclear cell clusters, was increased in the hMlkl-KI mice. Transcriptomic analysis revealed that MLKL overexpression altered the expression of genes involved in cellular senescence, inflammation, and drug metabolism. The increase in inflammation, necroptosis, and cellular senescence in the livers of 6-month-old hMlkl-KI mice was associated with an increase in liver fibrosis. The data from our study suggest that necroptosis has the potential of inducing inflammation through two pathways: (1) the initial inflammatory storm triggered by DAMPs released from necroptotic, dying cells and (2) SASP-factors produced by senescent cells that were induced by necroptosis.